A novel FAM83G variant from palmoplantar keratoderma patient disrupts WNT signalling via loss of FAM83G-CK1α interaction.
Description
Palmoplantar Keratoderma (PPK) is a multi-faceted skin disorder characterised by the thickening of the epidermis and abrasions on the palms and soles of the feet. Among the genetic causes, biallelic pathogenic variants in the FAM83G gene have been associated with PPK in dogs and humans. Here, a novel homozygous variant (c.794G>C, p.Arg265Pro) in the FAM83G gene, identified by whole exome sequencing in a 60-year-old female patient with PPK, is reported. The patient exhibited alterations in the hair and skin of both hands, dystrophic nails, thin, curly, and sparse hair, long upper eyelid eyelashes, and poor dental enamel. FAM83G activates WNT signalling through association with ser/thr protein kinase CK1α. When expressed in FAM83G-/- DLD1 colorectal cancer cells, the FAM83G (R265P) variant displayed poor stability, a loss of interaction with CK1α and attenuated WNT signalling response. These defects persisted in skin fibroblast cells derived from the patient. Our findings imply that the loss of FAM83G-CK1α interaction and subsequent attenuation of WNT signalling underlie the pathogenesis of PPK caused by the FAM83G (R265P) variant. We have analysed protein abundance in both DLD1 colorectal cancer cells and patient-derived fibroblasts using western blotting with antibodies against our proteins of interest and quantification by Fiji (ImageJ 1.53q). FAM83G-CK1 interactions were demonstrated using immunoprecipitation followed by western blotting. WNT signalling activity was measured by monitoring mRNA levels of WNT target gene Axin2 using qRT-PCR with primers amplifying Axin2 and GAPDH internal control.